The frequency of the third overtone of a closed end organ pipe equals the frequency of the fifth harmonic of an open end organ pipe. Ignoring end correction, the ratio of their lengths $$l_{open} \colon l_{close}$$ is

A

$$10 \colon 7$$

B

$$10 \colon 9$$

C

$$2 \colon 1$$

D

$$7 \colon 10$$